Not sure if this is helpful to anyone in this thread, but here's a one-liner that you can use to create those symlinks for ALL videos you may have stored in your little optified area.
I created a subdirectory called /opt/bootvideos and have been collecting ones I see on the forums there. I like the idea of symlinking to save rootfs space, so wrote this to help out create them all on the fly.
for i in /opt/bootvideos/*; do ln -s $i /usr/share/hildon-welcome/media/$(echo $i | awk 'BEGIN { FS="/" } ; { print $4 }'); done
The result is you get a directory that looks like this, and now can just use any video you want in your config file.
copied the Hands-video to /opt/media/, deleted the media-folder in /usr/share/hildon-welcome/ and made a sym-link from /opt/media/ to media/ in hildon-welcome - didn't work as well...
but everything is shown fine in x-term... every file is there where it's supposed to be :/
EDIT:
is it possible that if you changed the indicator_updateX.pngs to something else with bigger filesize that it's too much data and the n900 isn't able to buffer everything and so just skips the video? o.O
